The amazing upside down rainbow

This may look like a colourful smile in the sky - but in fact it's an upside down rainbow caused by freak weather.

This may look like a colourful smile in the sky - but in fact it's an upside down rainbow caused by freak weather.

The phenomenon, called a circumzenithal arc, is rarely seen outside the polar regions and is hardly ever spotted in the UK.

But delighted astronomer Dr Jacqueline Mitton caught it on film above her Cambridge home.

She said: "I've never seen anything like it before and I'm 60.

It was pretty impressive."

Normal rainbows are made when rays of sunlight penetrate raindrops and emerge from other side creating a prism of colours in an arc.

But if the sunlight strikes ice crystals high in the atmosphere at the right angle they are reflected back the way they came, creating a reverse rainbow.

Dr Mitton added: "The conditions have to be just right - you need the right sort of ice crystals and the sky has to be clear. It's quite surprising for this to occur somewhere like Cambridge, usually it is in places that are colder. We are not sure how big an area it was visible over."

The colours in Sunday's rainbow were intensified by the position of the sun, which was at the optimum spot in the sky of 22 degrees.

And the apparition was made even more dazzling by the presence of "sun dogs" - gleaming spots on a halo around the sun.

Dr Mitton said: "It was just an amazing combination of factors that happened at the right time."

Husband Simon, 62, an astronomy writer, said: "The circumzenithal rainbow is much brighter than a rainfall rainbow."

AND HERE'S THREE OTHER WEATHER PHENOMENA YOU DON'T SEE EVERY DAY..

FOGBOW

These are formed in the same way as rainbows but the water droplets are so fine that the light is no longer reflected. Instead it merges into a white glow rather than the bright colours of a rainbow.

MOONBOW

Just as the sun can make rainbows in the day, the moon produces them at night. A bright moon, near to full is needed. Moonbows are faint because the light lacks power. They are usually white.

AURORA BOREALIS

The flare ups are explosions of magnetic energy a third of the way between Earth and the moon. They happen when magnetic fields from Earth hit particles from the sun.

COLOURS OF THE RAINBOW ARE EASY TO REMEMBER WITH THE MNEMONIC 'RICHARD OF YORK GAVE BATTLE IN VAIN' - RED, ORANGE, YELLOW, GREEN, BLUE, INDIGO, VIOLET